Windows and doorways with arcuate or arched headers have long been popular architectural additions to homes and commercial buildings. Such windows and doorways typically include a wooden jamb that has spaced vertical side members joined at their top ends by a curved or arched wooden header. Although the vertical members of such jambs are easily fabricated, reliable economic methods of fabricating high quality arched wooden headers have long evaded woodworking craftsmen.
One traditional method of crafting arched headers has been to join a series of mitered wooden blocks at their ends to form the general shape of the arch. The curve is then cut with a band-saw from the joined blocks to form the arched header, which can then be machined if desired and secured to the upper ends of vertical door jamb members. Clearly, headers fabricated manually in this way exhibit a number of problems and shortcomings. The butt joints between the joined wooden blocks, for example, tend to separate over time due to temperature and moisture induced expansion and contraction of adjacent blocks. Further, such headers usually are not suitable for staining because the skewed relative orientations of the wood grain in adjacent blocks is not considered visually attractive. Consequently, arched headers fabricated in this traditional way often are limited to use in door and window frames that are to be painted.
A less manual method of fabricating arched headers has been to stack a plurality of thin wooden planks with adhesive applied between the planks to form a laminated board. The board is then placed atop a convex form and the ends of the board are forced down toward the ends of the form to bend the board around the form and thus produce a laminated arcuate wooden header. While this method indeed represents an improvement over manual fabrication techniques, it nevertheless exhibits certain inherent drawbacks. For example, bending the laminated board into an arcuate form with pressure applied downwardly on each end results in having upward pressure applied to the center portion of the board and little or no pressure applied intermediate the center portion and the ends of the board. As a result, the individual planks of the laminated board are prone to crack and are subject to a significant amount of surface friction and sliding motion between layers that interferes with proper compression of the lamina. In addition, the relatively thick adhesive tends to become trapped between individual lamina in excessive amounts due to surface imperfections in the lamina, ripples formed in the lamina during bending, and uneven application of pressure. As a result, the quality of products produced by this method is at best unpredictable and sometimes even unacceptable.
Another known method of forming arcuate wooden structures is a mass production operation in which hydraulic presses are used to form arches from laminated boards. In this method, an arcuate ram is forced with hydraulic pressure into a corresponding concave form with the laminated board being trapped and compressed between the ram and the form. While this method usually is capable of producing large quantities of headers, it is inherently unsuitable for custom work since the shape of the form and ram is unchangeable. In addition, this mass production method necessitates the use of exceedingly thin highly flexible lamina, which detracts from the appearance of the final product and adds to the cost. Many of the problems of cracking and uneven glue flow that are inherent in other prior art methods also are present with the hydraulic press method.
An improvement over these prior art methods is embodied in the device disclosed in applicant's own U.S. Pat. No. 4,967,816 wherein a plurality of arms are slidably mounted on radially extended spokes. The arms can be positioned on the spokes to define an arcuate shaped mandrel whereupon a wooden board of laminated planks is progressively bent around and held against the mandrel from one of its ends to the other. Even though this device and method is a significant improvement over previous offerings, it nevertheless embodies certain problems and shortcomings inherent in its own design. For example, the arms that extend outwardly from the spokes to form the mandrel tend to flex or bend slightly inwardly as the board is bent around the mandrel so that the mandrel surface becomes slightly cone shaped. This can result in less than desirable glue joints on one side of the finished arched structure because of reduced pressure on the smaller side of the slightly cone shaped mandrel. Also, each of the arms in this device must be carefully adjusted to extend outwardly from its spoke at a precise right angle in order that the mandrel formed by the arms exhibit a smooth continuous curve. Also, while semi-circles and slightly elongated ellipses can be formed with the device of applicant's previous patent, the formation of highly elliptical arches or of unusual shapes such as cathedral arches have proven impractical or even impossible to produce because of the highly uneven and asymmetrical forces imparted to the arms and spokes of the device when attempting to form such shapes.
Thus it is clear that a continuing need exists for an apparatus and method of forming arcuate wooden structural members such as headers for door and window jambs that overcomes the disadvantages and shortcomings of the prior art, that is capable of forming highly elliptical or unusually shaped arches, and that can be operated reliably and economically to produce arched wooden structures of a quality superior to that of structures produced by prior art methods and devices. It is to the provision of such an apparatus and method that the present invention is primarily directed.